Soap-making and bleaching process



United States PatentO SOAP-MAKING AND BLEACHING PROCESS Claims priority,applicationGreat Britain February 16, 1954 7 Claims. (CL Isa-41s NoDrawing.

This invention relates to the bleaching of soap, particularly thebleaching ofsoap with an alkali metal hypochlorite.

When a soap of good color is required to be produced it is necessary tobleach the oil from which the soap is made with a bleaching earth. Thebleaching of oils with a bleaching earth is, however, a laborious andcostly process involving filtering of the oil from the earth. It alsoinvolves a treatment of the spent earth to recover the considerableamount of oil which is absorbed by the earth during the treatment.Consequently, earth bleaching of oils is adopted in the soap-makingindustry only when it is desired to produce soaps of the very highestquality, for example, toilet soaps.

The bleaching of oils by treatment with chemical bleaching agentsfollowed by saponification to produce good colored soap or the bleachingof soaps from unbleached oils avoids the abovementioned disadvantages ofearth bleaching. As chemical'bleaching agents hypochlorites, and inparticular sodium hypochlorite, have been suggested. Such hypochlorites,however, do not'effectively bleach most oils, although in the case ofsome oils a certain amount of bleaching may take place at veryhighconcentrations of'hypochlorite. Also, theyare not effectiveinbleaching soaps from'some oils, suchas red palm oil, unless violentagitation, for example, agitation by a high speed impeller working in astream of soap, is employed. Also, unlessviol'ent agitation is employed,a soap capable of being-bleachedwith' hypochlorite'te'nds torevert toits unbleached color tin-standing; The .-degr'ee of agitation has'tovbesu'ch that it is not=possible to carry out hypoch-loritetreatment ofsoaps batchwis'e in the conventional soap-making kettles, but .requiresaspecial apparatus for pumpingia'stream of hypochlorite into a stream ofsoap and violently agitating'the two streams:

Also, in soap-making processes, the lye which. separates from thegrained soap has an-unspent alkali content which is usually higher inthe case of continuous processes than in the case of batch processes, asWell as any impurities such as dirt and coloring matter present in theoil prior to saponification. It is uneconomic to discharge this lye toglycerine recovery without recovering alkali. The unspent alkali in suchlye may be neutralized by mixing the lye with an oilhaving a high freefatty acid content. The free fatty acid in this oil :neutralizes thealkali to form a neutral oil-soap mixture. This neutral oil-soap mixturecontaining all the dirty impurities present in the original oil is thentreated, for example, by 'centrifuging to remove the major part of theaqueous con stituents and the dirty impurities. The oil-soap mixture isthen added to the oil being saponified in the continuous soap-makingprocess. Although most of the dirt and other impurities is removed fromthe oil-soap mixture before passing into the continuous soap-makingprocess, a certain amount of impurities is not removed and thereforeimpurities are continuously being fed back into the soap-making process.Over a period of time there is 2,892,348 Patented Aug. 13 1957 ICCaprogressive build-up of color throughout the continuous soap-makingprocess with consequent contamination of the soap produced. A state ofaffairs is often arrived at when treatment of the soap as such with mostknown processes based -on the use of hypochlorite fails to'bleach thesoap satisfactorily.

It is an object of the present invention to provide a process ofbleaching soaps with a hypochlorite which avoids the above mentioneddisadvantages.

The present invention provides aprocess of preparing light-colored soapwhich includes the steps of contacting an oil, containing free fattyacid and from which the soap is to be formed, with a chlorite, thensaponifying the'chlorite-treated oil with alkali and bleaching theresultant soap with ahypochlorite.

The chlorite may be an alkali metal chlorite, such as sodium orpotassium chlorite, and is preferably added to the oil in the form of anaqueous solution. Likewise the hypochlorite may be an alkali metalchlorite such as sodium or potassium hypochlorite, and is preferablyadded'to'the oil in the form of anaqueous solution. desired,thehypochlorite and chlorite may be formed in situ-in the soap and oilrespectively, for example, in the case of the hypochlorite, by addinganalkali, such as sodium hydroxide, to the soap and' passing chlorinegas'through it.

The process of the invention may be used for bleaching soapsfrom anyvegetable or animal oils containing free'fatty acids; that is to say, itcanbe used for so'aps from unrefined oils which generally'cont'ain freeacids: It is of particular advantage for decolorizing soaps-made fromoil blends which include the acid oils resulting from the splitting ofsoapwhen the soapstock obtained from crude oils are alkali refined.

When adding the chlorite to the oil and the hypo chlorit'e to the soapit is not necessaryto provide violent agitation. In fact, agitation needonly be sufficient to insure'uniform dispersion of the additivesthroughout the oil and soap respectively. This is in contrast tothe casewhere hypochlorite' is'usedto bleach soaps from oils not treated withchlorite where violent agitation of a stream of'hypochlorit'e and astream of soap is essential. The fact that agitation of thesoapandhypochlorite does not have to be violent, and does not involve theuse of streams means-that'the operations of treating the oil withchlorite, saponifying and treating the soap with hypochlorite may becarried outin a single vessel, for example,a soapmaking kettle;insoapmaking may be used for saponification. 'For example, the alkalimetal hydroxides such as sodium and potassium hydroxide can be used toproduce-water soluble soaps whereas alkaline-earth metal hydroxides suchas calcium and barium hydroxide canbe used'toproduce water insolublesoaps. Such a vessel should preferably be acid-resistant since theproduct of the chlorite addition may. attack non-resistant materials andthis may, result in lessJeflicient' decolorization of the finished soapthan'would otherwise be obtained. The saponification procedure isconventional.

The amount of chlorite used may be between 0.1% and "10% based'onthetotal Weight of oil and fatty acid to "be" reacted with alkali; For'bestresults the amount of chlorite should 'be 0.5%. The amount of aqueoushypochlorite-(l4% available chlorine) used is preferably betweenv0.2-5%and 20%, i. e., from about 0.04 to 3% of hypochlorite expressed asalkali metal hypochlorite, based on thetotalweight of oil and fattyacid'previously treate'dwith chlorite and for best results 7.5% ofaqueous hypochlorite should 'be used. The temperature ofboth" thechlorite treatment and the hypochlorite bleaching should bev between40C. and 100 C. and preferably about C. The time of contactshouldbebetween-d- Any alkali customarily used minutes and 300 minutesand preferably about 30 minutes, when carrying out the process of theinvention batchwise. It is preferred to keep the time of contact betweenthe soap and hypochlorite as short as possible. In one embodiment of theinvention suitable for use in combination with a continuous soap-makingprocess, a stream of soap made from chlorite-treated oil containing freefatty acid may be mixed by a suitable form of mixing device with astream of aqueous solution of hypochlorite. No violent agitation of thesoap and hypochlorite is necessary to give a bleached soap, the color ofwhich shows less tendency to deteriorate on standing than do soapsbleached by hypochlorite alone.

In copending application Serial No. 481,709, filed January 13, 1955,there is described a process of bleaching soapstocks obtained in thealkali-refining of animal and vegetable oils, which process consists oftreating the soapstock with a hypochlorite and a chlorite.

The process of the present invention is particularly suitable forcombining with the process of the aforesaid copending application. Inone embodiment of the present invention soapstock treated according tothe process of the copending application may be mixed with thechlorite-treated oil containing free fatty acids prior to the reactionwith alkali. Such soapstock which contains a considerable proportion ofneutral oil is thus directly used in a soap-making process. Hitherto ithas been necessary to split such soapstock with mineral acid to covertit into an acid oil by a difiicult and prolonged process, and the acidoil so produced was utilized in the soap-making process. In carrying outthis specific embodiment of the process of the present invention thesoapstock may be decolorized by the process of the copending applicationprior to mixing with the chlorite-treated oil utilized in the presentinvention. Alternatively, the untreated soapstock and material which isto be chloritetreated may be mixed and chlorite and hypochlorite addedto the mixture provided the amount of soapstock in the mixture issufiicient to render the mixture neutral or alkaline. The soap formedafter reaction with alkali in this embodiment of the present inventionhas then, of course, to be treated with hypochlorite.

The process of the present invention is also particularly useful inovercoming the color build-up resulting from the incorporation of theproducts of neutralization of the lye encountered in the soap-makingprocesses, and which is not overcome by the hypochlorite treatment ofsoap even when this treatment involves intense agitation such as ismentioned above.

The invention will now be illustrated by the following examples, inwhich Lovibond color unit readings were obtanied by dissolving the soapsformed in various examples in 70% by volume ethyl alcohol to obtain a byweight of alcoholic soap solution, on which Lovibond color measurementswere then made in a 2 inch cell. Parts are by weight.

Example 1 This illustrates the treatment of a crude oil blend to whichsoapstock has been added. An oil blend of the following composition wasprepared:

Parts Crude palm oil 35 Crude palm kernel oil 35 Crude mixed split acidoils 10 blend alkaline and the free fatty acid content of the finalblend was 20.6% expressed as oleic acid.

One hundred (100) parts of this oil blend were treated at C. in areaction vessel fitted with a stirrer with 0.5 parts of sodium chloritein the form of an aqueous solution of about 50% concentration. Treatmentwas continued for about 30 minutes. Soap was then prepared bysaponification with caustic soda in the normal manner. The lye wasallowed to separate and was then removed. The soap was washed and thewashings removed. To the soap which had about 60% total fatty matter wasadded 15% by weight of water and 5% by weight based on the weight of thesoap treated (equivalent to about 8.3% by weight of the total fattymatter) of sodium hypochlorite liquor having about 14% by weightavailable chlorine. The mixture was contained in a glass (or suitablychemically-resistant reaction vessel) fitted with a stirrer and washeated to 60 C. and held at that temperature for about 15 minutes inwhich time stirring had been taking place. The blended soap was thentreated in the usual manner for soap finishing operations. Lovibondcolor measurements on a 10% alco holic soap solution were then made andare given in the following Table I, which also gives Lovibondmeasurements made on soaps obtained by saponifying respectively anuntreated oil blend, an oil blend treated with 5% bleaching earth andthe oil blend treated with 10% hypochlorite only:

The above figures clearly illustrate the better bleaching elfect on soapof the process of the invention over soap from oil treated with 10%hypochlorite and from earth bleached oils.

Example 2 Soaps prepared in a similar manner to that of the last line ofthe above table were kept for 12 and 15 days, respectively, at 35 C. and75% relative humidity. Lovibond readings on 10% alcohol soap solutionsof samples were taken before and after standing. These readings aregiven in the following tables, those in Table II relating to storage for12 days and those in Table III to storage for 15 days:

TABLE II Lovibond Readings on Alcoholic Soap Solutions Yellow Red Soapbefore storage 0.9 0. 2 Soap after 12 days storage 1. O 0. 2

TABLE III Lovibond Readings on Alcoholic Soap Solutions Yellow Red Soapbefore storage 1. Soap after 15 days storage 1.

These figures clearly illustrate the absence of color reversion in soapsformed according to the invention.

Example 3 This illustrates the formation of hypochlorite in situ. An oilblend was prepared with the following composition:

Parts Crude palm oil 24.0 Crude tallow 22.5 Crude palm kernel oil 24.0Crude mixed soft acid oil 9.5

soap was prepared from the treated oil blend, also in the,

manner described in Example 1. The soap was then mixed with about of itsweight of water containing the requisite amount of sodium hydroxidewhich when reacted with chlorine would form the equivalent of about 5%of the weight of soap (having 60% total fatty matter) of sodiumhypochlorite liquor having about 14% by weight available chlorine. Thismixture was heated to 60 C. and passed through a suitable enclosedmixing apparatus, for example, a centrifugal or other suitable pump. Thenecessary amount of chlorine gas to react with sodium hydroxide to formthe equivalent of about 5% of the sodium hypochlorite liquor (14% byweight available chlorine) based on the weight of soap having a 60%total fatty matter, is fed into the stream of soap/ sodium hydroxidemixture entering the mixing apparatus, for example, into the inlet sideof the pump. The bleached soap passes continuously from the outlet ofthe mixing apparatus and is then subjected to the normal finishingoperations for the production of soap. Analogous experiments werecarried out with concentrated oil blends and the results obtained areexpressed in the fol- The oil treated according to the present inventioncan be any of those customarily used in making soap. Examples ofpreferred fatty oils are rapeseed oil, peanut oil, palm oil, coconutoil, tallow, olive oil, palm kernel oil and like oils.

I claim:

1. A process of preparing light-colored soaps which includes the stepsof contacting a glyceride oil containing free fatty acid with an alkalimetal chlorite, saponifying the chlorite-treated oil with alkali andbleaching the resultant soap with from about 0.04% to about 3% of analkali metal hypochlorite based on the total weight of chlorite-treatedoil.

2. The process of claim 1 in which the chlorite is sodium chlorite andthe hypochlorite is sodium hypochlorite.

3. A process of preparing light-colored soaps which includes the stepsof contacting a glyceride oil containing free fatty acid with from about0.1 to 10% of an alkali metal chlorite based on the weight of oil,saponifying the chlorite-treated oil with alkali and bleaching theresultant soap with from about 0.04% to about 3% of an alkali metalhypochlorite based on the total weight of chlorite-treated oil.

4. The process of claim 3 in which the oil is contacted with an aqueoussolution of chlorite at a temperature between about 40 and C.

5. The process of claim 4 in which the said chlorite is sodium chloriteand the hypochlorite is sodium hypochlorite.

6. A process of preparing light-colored soap which includes the steps ofcontacting a glyceride oil containing free fatty acid with an aqueoussolution of an alkali metal chlorite at a temperature between about 40and 100 C., saponifying the chlorite-treated oil with alkali andbleaching the resultant soap by contact with an aqueous solution of analkali metal hypochlorite at a temperature between about 40 and 100 C.,said aqueous solution of alkali metal hypochlorite furnishing from about0.04% to about 3% of an alkali metal hypochlorite based on the totalweight of chlorite-treated oil.

7. The process of claim 6 in which the chlorite is sodium chlorite andthe hypochlorite is sodium hypochlorite.

References Cited in the file of this patent UNITED STATES PATENTSKauffmann Jan. 13, 1942 Stossel et a1 Dec. 2, 1947 Henderson et a1 Oct.4, 1949 OTHER REFERENCES

1. A PROCESS OF PREPARING LIGHT-COLOURED SOAPS WHICH INCLUDES THE STEPSOF CONTACTING A GLYCERIDE OIL CONTAINING FREE FATTY ACID WITH AN METALCHLORITE, SAPONIFYING THE CHLORITE-TREATED OIL WITH ALKALI AND BLEACHINGTHE RESULTANT SOAP WITH FROM ABOUT 0.04% TO ABOUT 3% OF ALKALLI METALHYPROCHLORITE BASED ON THE TOTAL WEIGHT OF CHLORITE-TREATED OIL.